Physical pain from hunger
I don't think I ever felt actual hunger before this either. It was odd. I was like oh crap do I have an ulcer? etc all the worst jumped to my mind. I ate it went away. It's happened enough times now that I figure it has to be hunger as every time eating makes it go away. Good luck and try to avoid it. I find when I do get to that point I've been known to eat too fast and paid for it!
It is possible that it is your body's response to hunger, but keep an eye on it. It could possibly be an ulcer. Not to scare you, but ulcers are more painful when your stomach is empty. I have gone through this. I thought it was hunger. If I take an Omeprazol (sp?) every morning, I don't have any problems. Consult your doctor if you are worried or if the pain is intense.